Type III group B streptococci (GBS) are an important cause of neonatal sepsis and meningitis and like many bacterial pathogens produce capsules which retard opsonization via the alternate complement pathway which prevent efficient phagocytosis. The type III polysaccharide capsule is a linear polymer of glucose (glu), glucosamine (glm) and galactose with galactose substitutions which are modified by sialic acid. Sialic acid residues account for the antiphagocytic nature of the capsule and are required for full virulence. Density and size of the capsule varies considerably both within a culture and between strains and this is purported to influence virulence of a given culture. Although a poor antigen, capsule polysaccharide can induce protective immunity.